Drill-collar construction

ABSTRACT

A drill-collar construction for use in rotary drilling of wells. The individual collars are joined end-to-end with connectors which have greater fatigue resistance than the steel of the drill collars. The preferred metal for the connectors is titanium or a titanium-base alloy.

United States Patent Fletcher Redwine Irving, Tex.

Dec. 31 1968 Mar. 30, 197 1 United States Steel Corporation Inventor Appl. No. Filed Patented Assignee DRILL-COLLAR CONSTRUCTION 2 Claims, 1 Drawing Fig.

US. Cl 285/ 173, 285/333,175/320 Int. Cl F161 15/00, E2lb 17/02 Field of Search 285/ 329,

422, 114 (Cursory), 115 (Cursory), 390 (Curso y); 175/320; 29/(lnquired); 285/333, 334, 173

[56] References Cited UNITED STATES PATENTS 2,536,216 l/l951 Powell 285/333X 2,941,784 6/1960 Martin l75/320X 2,955,847 10/1960 McKenna 285/329X 3,083,043 3/1963 Thomhill 285/333 3,126,214 3/1964 Wong et al 285/333X OTHER REFERENCES Esco Catalog 504, Nov. 1967, 4 pages (Copy in class 285 subclass 422) Primary Examiner-Thomas F. Callaghan Attorney-Walter P. Wood ABSTRACT: A drill-collar construction for use in rotary drilling of wells. The individual collars are joined end-to-end with connectors which have greater fatigue resistance than the steel of the drill collars. The preferred metal for the connectors is titanium or a titanium-base alloy.

mvE/v ran. FL ETCHER nsowuvs a A! rarney PATENTED man IQYI DRILL-COLLAR CONSTRUCTION This invention relates to an improved drill-collar construction for use in rotary drilling of wells.

When a well is drilled with conventional rotary equipment, the drill bit is attached to the lower end of a string of drill pipes, down which drilling fluid circulates. The portion of the drill string immediately above the bit is made up of a series of drill collars", which are heavy-walled pipe sections, each usually about 30 feet long, joined end-to-end. The purpose of drill collars is to supply the necessary weight to the bit to enable it to penetrate the earth formation. The harder the formation, the more weight required and the larger the number of drill collars needed. The drill collars are in compression, but the rest of the drill string should be in tension. The point of neutral stress should be located in the drill collars near the upper end of the series. Although drill collars are relatively inflexible, uneven drilling feed, changes in the earth formation, slanted formations, etc., as well as shifts in the neutral stress location, cause them to flex to some extent. Such flexing takes place mostly at joints between individual drill collars. Most drill collar failures are the result of fatigue at these joints.

An object of my invention is to provide an improved drillcollar construction which forestalls fatigue failures at joints between individual collars.

A more specific object is to provide an improved drill-collar construction in which the individual collars are joined to one another through connectors of material highly resistant to fatigue, for example titanium or a titaniumbase alloy.

in the drawing:

The single FIGURE is a longitudinal vertical section of a pair of drill collars and a connector in accordance with my invention.

The drawing shows portions of two drill collars and 10a of seriesand a connector 12 which joins the two collars endto-end. Similar connectors are used between other collars of the series, not shown. The collars may be externally threaded and the connector internally threaded as illustrated (pin-andpin), or the collars may be internally threaded and the connector externally threaded (box and-box), or opposite ends of the connectors may be threaded externally and internally (combination). Commonly each collar is about 30 feet long, and

each connector about 12 to 18 inches. The collars usually are of an alloy steel heat treated to provide a tensile strength of about 125,000 p.s.i., and a modulus of elasticity of about 29 million to 30 million p.s.i. Such collars have a wet fatigue strength in drilling mud of about 13,000 p.s.i.

in accordance with my invention, 1 form the connector 12 of a metal which has a tensile strength comparable to the steel of the drill collars 10 and 10a, but a substantially lower modulus of elasticity and greater fatigue resistance. My preferred metal for this purpose is titanium. I intend the term titaniurn" to include various titanium-base alloys, such as that which contains 6 percent aluminum, 4 percent vanadium, and the balance titanium, or those which contain small percentages of other known alloying elements including tin, zirconium, molybdenum, iron, chromium, etc. Typically the metal used in the connector has a modulus of elasticity of about 16,200,000 p.s.i. and a wet fatigue strength in drilling mud of 95,000 p.s.i.

With my invention, any flexing in the series of drill collars takes place in the connectors, rather than in the drill collars themselves. Since these connectors have much greater fatigue resistance, fatigue failures are forestalled. Corrosion may take place in fatigue cracks. My invention provides prevents such corrosion, both by preventing fatigue cracks from forming and by use of a metal which is highly resistant to corrosion. Thus, my invention effectively prolongs the life of drill collars.

lclaim:

1. In a drill string for use in rotary drilling of a well, a series of drill collars and short-length connectors threadedly engaged with the ends of said collars and joining them end-toend, said collars being'formed of an alloy steel which has a relatively high modulus of elasticity and low fatigue strength, said connectors being formed of titanium which has a lower modulus of elasticity and a higher fatigue strength, whereby flexing in the series of drill col ars takes place In said connectors rather than in the collars themselves.

2. A series of drill collars as defined in claim 1 in which the collars themselves have a modulus of elasticity of about 29 million to 30 million p.s.i. and a wet fatigue strength in drilling mud of about 13,000 p.s.i., and said connectors have a modulus of elasticity of about 16,200,000 p.s.i. and a wet fatigue strength in drilling mud of about 95,000 p.s.i. 

1. In a drill string for use in rotary drilling of a well, a series of drill collars and short-length connectors threadedly engaged with the ends of said collars and joining them end-toend, said collars being formed of an alloy steel which has a relatively high modulus of elasticity and low fatigue strength, said connectors being formed of titanium which has a lower modulus of elasticity and a higher fatigue strength, whereby flexing in the series of drill collars takes place in said connectors rather than in the collars themselves.
 2. A series of drill collars as defined in claim 1 in which the collars themselves have a modulus of elasticity of about 29 million to 30 million p.s.i. and a wet fatigue strength in drilling mud of about 13,000 p.s.i., and said connectors have a modulus of elasticity of about 16,200,000 p.s.i. and a wet fatigue strength in drilling mud of about 95,000 p.s.i. 